An unstretched polyester sheet is amorphous and excellent in transparency, so that the sheet is suitable for punching and bending. Therefore, with a heat-molding method, the polyester sheet is used for a wide range of applications including an outer transparent container such as a container for food and medicine, a blister pack for sundry goods, and a clear case.
A polyester sheet used as a material for molding and processing these packaging containers is cut into pieces, each of which has a predetermined width and length. Then, the cut pieces are stacked with one another to be supplied to a printing machine or a molding and processing machine one by one. However, when the sheet is poor in sliding properties and is subjected to blocking, it becomes difficult to surely supply the pieces of the sheet one by one. Sometimes a plurality of pieces are supplied at one time or in a misaligned state due to blocking. Accordingly, workability is lowered, and a defective rate of the molded and processed articles is increased.
A number of molded and processed packaging containers are stacked with one another for transportation. When commercial goods are packed in the packaging container, each of the stacked packaging containers needs to be picked up one by one. However, if the sheet material itself is poor in sliding properties or is subjected to blocking, it is not easy to smoothly pick out one from the stacked packaging containers. Sometimes several packaging containers are picked up at one time in an overlapped manner.
To solve the above problems, it is effective to improve surface properties of a sheet and further a molded article thereof so as to be smooth for sliding.
Specifically, to improve sliding properties, there are proposed a method in which a lubricant such as a silicone compound is applied on a sheet surface, and a method in which inorganic particles are added so that a sheet surface has microscopic asperity.